When a person in the vicinity of a camera or a part (a hand, for example) of such a person is imaged as a subject, for the purpose of monitoring the state or action of the person, it is effective to remove the background and extract the region which the subject occupies, and analyze the extracted region in detail. Patent reference 1 discloses a display imaging apparatus which periodically turns on and off the illuminating light for irradiating the subject, at a short interval, and obtains the captured image during the on-period, and the captured image during the off-period, and uses the difference between them to extract the region of the subject in the vicinity the camera.
A problem associated with this method is that when the background changes or the subject moves, a region of false signals may appear in the difference image. To cope with this problem, Patent reference 1 discloses generating an interpolated image in which the movement of the subject or the background has been compensated for, and generating a difference image, from which the regions of false signals due to movement of the subject have been removed. Also, Patent reference 2 discloses an image processing apparatus which detects the movement amount of the subject, and uses the detected movement amount for the identification of the subject region.